Section I: The research proposal focuses on the placental lactogen/prolactin (PL/PRL) gene family. Our research has shown that there are two principal types of PL in the rat; rPLI, secreted days 8-14, and rPLII secreted days 12-21. By cDNA cloning we have shown that rPLII is structurally related to PRL's. Recent experiments have led to the discovery of at least 4 other unsuspected PRL/PL like proteins. We propose to determine nucleotide sequence of these new family members. Although an endocrine function for PL and PRL in the non-lactational state has not been well defined, the recent observation in our laboratory of expression of prolactin-like RNA transcripts in a variety of tissues including heart, kidney, ovaries, etc. suggests that the PRL/PL related peptides may have important autocrine or paracrine actions. Further, we have cloned two genes (pK5 and pK25) from a rat kidney GT10 cDNA library, using rPRL cDNA as a probe. One of these kidney clones, pK25 codes for a unique mRNA which is not expressed at all in the kidney of the non- pregnant rat. This discovery of a pregnancy specific, PRL-related mRNA in the kidney may provide important insights into the hormonal changes involved in salt and water balance in pregnancy. The characterization, functional role and regulation of the PL/PRL gene products will be studied after expressing the protein in E. coli. To study rPLI, the other major PL, we have partially purified it and raised antibodies which will be used to select rPLI clones from an expression library. These will be sequenced and characterized as the other placental clones. We have identified both maternal pituitary and ovarian factors which inhibit, and fetal factors which stimulate rPL-II secretion. We propose to identify the chemical nature of these regulatory factors and study their effects in some detail. Section II. We propose to use the No2 cell to identify, purify and characterize tissue and serum factors (synlactins) which enhance or modulate the action of PRL. Similarly, we have identified several breast cancer cell lines which secrete a PRL-like factor. The further identification and characterization of these PL/PRL factors that stimulate No2 cell proliferation is proposed. These factors may act in a paracrine or autocrine fashion to induce proliferation of breast cancer cells or lactational changes in patients with galactorrhea and normal PRL levels.